1. Field of the Invention
The present invention relates to a substrate for lithographic printing plates and a presensitized plate for use in making lithographic printing plates (hereinafter referred to as "PS plate") which comprises the substrate and more particularly to a substrate for lithographic printing plates which has good adhesion to a light-sensitive layer and can impart high sensitivity to the resulting PS plates and high printing durability to the resulting lithographic printing plate as well as a PS plate comprising the substrate.
2. Prior Art
In the printing industries, the PS plate has been one of the leading mainstreams of printing plates, because the handling thereof is very easy and the use thereof contributes to the reduction of labor required for making a printing plate and for printing and has widely been used in, for instance, usual commercial printing, newspaper-printing, form printing and printing of paper wares.
Recently, there has been an increased demand for further speeding up of and labor-reduction in the plate-making and printing processes. Under such circumstances, there have been proposed new plate-making systems and automated plate-making systems and correspondingly there have been desired for the development of PS plates excellent in sensitivity and developability, which are adapted to these new plate-making systems. For instance, when images are to be formed on a PS plate in a conventional method, an original film is brought into close contact with the PS plate under vacuum and then the assembly is irradiated with light, but in recent practice, there has been used a method for forming images which comprises imagewise exposing the PS plate by directly projecting enlarged images through a microfilmed original. In addition, there has also been adopted a method for forming images on a PS plate which comprises directly scanning a laser beam such as an argon ion laser beam, visible light rays or ultraviolet rays on the PS plate for imagewise exposing the same.
However, such PS plates must have extremely high sensitivity as compared with those conventionally used in order to form images by the foregoing new exposure methods. In addition to the requirement for the improvement in the sensitivity, there has been desired for the improvement in developers. More specifically, the conventional developers mainly comprise organic solvents, but they are unfavorable from the viewpoint of, for instance, safety of working environment and cost for developing treatments and, therefore, there has recently been desired for the development of developers mainly comprising aqueous solution systems.
To obtain a PS plate having high sensitivity, the light-sensitive layer on image areas must be strongly adhered to the surface of a substrate, the PS plate must be able to provide a lithographic printing plate having high printing durability and the non-image area obtained after development must be hardly contaminated.
To improve the adhesion between a light-sensitive layer and a substrate, there have been proposed a variety of methods, for instance, a method comprising anodizing a substrate in a phosphoric acid solution as disclosed in Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J.P. KOKOKU") Nos. Sho 46-26521, Sho 55-12877 and Sho 54-37522 and Japanese Unexamined Patent Publication (hereinafter referred to as "J.P. KOKAI") No. Sho 62-99198; a method comprising anodizing a substrate in a mixed acid solution of phosphoric acid and sulfuric acid as disclosed in J.P. KOKAI Nos. Sho 55-28400 and Sho 53-2103, U.S. Pat. No. 4,049,504 and Brit. Patent No. 1,240,577; a method comprising anodizing a substrate in a phosphoric acid solution and then further anodizing in an organic acid solution of, for instance, polyvinylsulfonic acid or phytic acid as disclosed in J.P. KOKAI Nos. Sho 57-89497 and Sho 57-89498 and U.S. Pat. No. 4,022,670; and a method comprising anodizing a substrate in a phosphoric acid solution and then anodizing it in an inorganic acid solution of, for instance, sulfuric acid or boric acid instead of an organic acid as disclosed in J.P. KOKAI No. Sho 59-193298 and J.P. KOKOKU No. 46-43123. Further, well-known are those methods comprising anodizing a substrate in an electrolyte of a phosphate compound such as Na.sub.3 PO.sub.4, NaH.sub.2 PO.sub.4 and Na.sub.2 HPO.sub.4 as disclosed in J.P. KOKAI Nos. Sho 60-56073, Sho 59-15644 and Sho 60-52596 or combination thereof. However, all of these methods use phosphate compounds and, therefore, eutrophication of drainage systems is unavoidable. Further, this becomes a cause of brown tide and the putrefaction of lakes or the like and is undesirable from the viewpoint of environmental assurance. For this reason, there has been desired for the development of a solution which can be replaced with those mainly comprising phosphate compounds, i.e., a solution free of phosphate compounds used in the anodization.
When a positive-working PS plate which comprises a positive-working light-sensitive layer containing o-quinone diazide is formed by applying a positive-working light-sensitive layer containing o-quinone diazide onto the surface of an aluminum substrate which have been anodized by the method as described above, the non-image area obtained therefrom is colored after development. To solve this problem, there has been proposed a method in which an aluminum substrate is treated with a condensed sodium arylsulfonate (see, for instance, J.P. KOKAI No. Sho 57-195697). This method makes it possible to prevent the coloration of non-image area, but on the contrary, the printing durability of the resulting lithographic printing plate is impaired.